With recent advancement of digital technologies, electronic hardware such as portable information devices and information home appliances has been developed to provide higher functionality. As the electronic hardware has been developed to provide higher functionality, development of miniaturized and higher-speed semiconductor elements incorporated into the electronic hardware is progressing at a high pace. Among them, the use of a large-capacity nonvolatile memory which is represented by a flash memory has been spreading at a rapid pace. Furthermore, as a next-generation new nonvolatile memory which has a potential to replace the flash memory, a resistance variable semiconductor memory device (ReRAM) including a so-called resistance variable element has been researched and developed. As defined herein, the resistance variable element refers to an element which has a characteristic in which its resistance values change reversibly in response to electric signals and is able to store information corresponding to the resistance values in a nonvolatile manner. Unlike a phase change random access memory (PCRAM) which is adapted to change its resistance values due to a fact that a change of a crystalline state is induced by heat generated by electric stresses applied thereto, the resistance variable element changes its resistance values by changing redox states of a resistance variable material, directly in response to the electric stresses applied thereto, i.e., by migration of electrons.
As an example of a large-capacity semiconductor memory device incorporating the resistance variable element, a cross-point semiconductor memory device has been known. In the cross-point ReRAM, a nonvolatile memory element (also referred to as memory cell) is configured to incorporate as a current controlling element, a diode connected in series with a resistance variable element provided at a cross-point where a word line three-dimensionally crosses a bit line, to avoid reading of a resistance value from a certain resistance variable element from being affected by another memory elements belonging to another rows or columns (e.g., see patent literature 1).
FIG. 13 is a view showing a semiconductor memory device incorporating a memory cell including a conventional resistance variable element and a current controlling element. As shown in FIG. 13, in a cross-point memory cell array including bit lines 210, word lines 220 and memory cells 280 formed at cross-points of the bit lines 210 and the word lines 220, each memory cell 280 is configured by connecting a resistance variable element 260 adapted to store data by an change in its electric resistances due to electric stresses in series with a two-terminal current controlling element 270 having a non-linear current-voltage characteristic in which the current controlling element 270 is capable of flowing a current bidirectionally. The bit line 210 which serves as an upper wire is electrically connected to the current controlling element 270. The word line 220 which serves as a lower wire is electrically connected to the resistance variable element 260. Since a current flows bidirectionally through the current controlling element 270 when data is rewritten in the memory cell 280, a larger capacity is attainable by using, for example, a current controlling element (varistor or the like) having a current-voltage characteristic which is symmetric bidirectionally (both of positive voltage side and negative voltage side) and is non-linear.